We've found out that we are pregnant (about 10 weeks) and have a 2 week trip in Thailand. (A few of the Islands).

The date of departure is mid December.

I'm having a hard time understanding what the advice is surrounding current Zika outbreaks in Thailand.

I am not someone who is easily taken back by all of the fear, uncertainty and doubt that you read online, but my partner is and the midwife recommended against all travel.

The cost of the holiday is obviously quite expensive (about 5k GBP) and if the advice is just advisory because there IS a risk, well that is something to factor. There's risk in everything we do.. I just can't find any stats about how many outbreaks per week~, is the risk high, meaning, 2% chance?.. Or high as in 99%.. you will get Zika..

  • When during pregnancy will Zika cause harm to baby?
  • Do 100% of all bites lead to Zika? Is it likely we have a immunity? Or are not all mosquitos carriers?
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    @JonathanReez fairly common colloquial usage by English native speakers.
    – CMaster
    Commented Oct 7, 2016 at 7:59
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    To be honest, I suspect you have found plenty of legitimate advice explaining why it's a terrible idea to take this kind of risk and are looking for people here to tell you that things aren't so bad by twisting some statistics, all because you don't want to be out 5K. Exactly what percentage chance of birth defects are you willing to risk here? And do you imagine you'll still have a fun vacation with this kind of doubt and paranoia constantly on your mind?
    – Lilienthal
    Commented Oct 7, 2016 at 9:22
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    @Lilienthal I'm not sure I'd agree its a "terrible" idea - yes there's a risk, but we don't know what the OPs risk profile is like in normal life. It may actually be safer for them in Thailand.
    – CMaster
    Commented Oct 7, 2016 at 10:14
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    I'm visiting from Biology.SE and work on mosquito-borne viruses like Zika. Essentially, there is probably Zika in Thailand (see e.g. theguardian.com/global-development/2016/sep/30/…) and whether it's an acceptable level of risk is a decision you have to make, but if you go bednets will be essentially useless as Aedes are day-biting. You need to get some DEET-containing mosquito repellent, as strong as possible, and reapply regularly (including to clothing, otherwise they just bite through).
    – tardigrade
    Commented Oct 7, 2016 at 13:48
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    If you repost some of this (especially "Do 100% of all bites lead to Zika? Is it likely we have a immunity? Or are not all mosquitos carriers?") over on Biology.SE I'd be happy to give a detailed answer, but it's probably a bit off-topic here. That said, medical advice is strictly off-topic on Biology.SE so you'd have to be clear that you weren't considering it as such.
    – tardigrade
    Commented Oct 7, 2016 at 13:49

4 Answers 4


Let's start with the bad news ...

Zika has been found in SE Asia since the 1960s (the disease was first identified in the late 50s) but only recently has become the darling pandemic of the news media.

Cases of Zika caused Microcephaly have been reported in Thailand in recent months.

Clusters of Zika infections have been recorded in parts of Thailand in recent months.

Let's add in a dose of reality in the tropics ...

Zika is just one of several nasty tropical diseases that are endemic to SE Asia, including Dengue, Japanese Encephalitis, Malaria. All are mosquito borne, but via different species of mosquitoes.

Let's allow some light through the dark clouds ....

Viruses like Dengue and Zika are live transmissions, the mosquito females bite an infected person then transmit the disease to the next person they bite. This causes outbreaks to be localized, as the mosquitoes can not carry the infected blood very far (they don't fly worth beans with a partially full belly).

Using mosquito repellent to avoid being bitten, eliminates a substantial portion of risk in contracting any of the diseases I mentioned. But keep in mind that the Aedes species of mosquitoes (the ones transferring Dengue and Zika) are day biters, so you need to use repellent anytime you plan to be sitting outdoors. And just because your hotel has no mosquito harboring plants or pools, you never know what is in the neighbors yard next door, so use it even sitting around outside at your hotel.

December is dry season for most of Thailand, so the mosquito population is diminished, but not totally gone.

The number of Zika cases reported versus the population of Thailand is minuscule.

Effects on your unborn child ...

Ultimately, you and your doctor (or a tropical medical specialist) should discuss the potential effects of Zika on your unborn child at various stages of its development. We are not medical specialists here on this website.

  • Zika has been found in SE Asia since the 1960s interesting claim, do you have a reference ?
    – blackbird
    Commented Oct 7, 2016 at 13:06
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    The line about "mosquitoes can not carry the infected blood very far" is misleading about the biology (they're not a risk while they're still digesting the blood meal) but actually most adult Aedes do not tend to fly far (a few hundred metres). It's not accurate to say that "therefore most outbreaks are localised" though; mosquito-borne viruses can spread really fast.
    – tardigrade
    Commented Oct 7, 2016 at 13:47
  • @tardigrade - So far the reported outbreaks here in Thailand have been localized. And yes while mosquito borne illnesses as a whole can spread rapidly, this question is about Zika in Thailand.
    – user13044
    Commented Oct 8, 2016 at 0:36
  • Another piece of perspective: Thailand probably has tens of thousands of pregnant women at any given moment. If they can give birth to healthy children, so can your wife.
    – JonathanReez
    Commented Oct 8, 2016 at 6:27

The US Centers for Disease Control and Prevention has comprehensive coverage of the Zika virus, including destination-specific information.

It has an section devoted to pregnancy in which it notes:

What we know

  • Zika virus can be passed from a pregnant woman to her fetus.
  • Infection during pregnancy can cause certain birth defects
  • Zika primarily spreads through infected mosquitoes. You can also get Zika through sex.
  • There is no vaccine to prevent or medicine to treat Zika.

What we do not know

  • If there’s a safe time during your pregnancy to travel to an area with Zika.
  • How likely it is that Zika infection will affect your pregnancy.
  • If your baby will have birth defects if you are infected while pregnant.

The UK Travel Health Pro has the following alert for Thailand:

Zika virus in Thailand
This country is considered to have a high risk of ZIKV transmission. Increasing or widespread transmission has been reported. Pregnant women are advised to postpone non-essential travel until after pregnancy. Details of specific affected areas within this country are not available.


  • All travellers should avoid mosquito bites particularly between dawn and dusk.
  • There is no vaccination or medication to prevent ZIKV infection.
  • It is recommended that pregnant women planning to travel to areas with a high risk of ZIKV transmission should postpone non-essential travel until after pregnancy.
  • Women should avoid becoming pregnant while travelling in, and for 8 weeks after leaving an area with active ZIKV transmission.
  • If a woman develops symptoms compatible with ZIKV infection, it is recommended she avoids becoming pregnant for a further 8 weeks following recovery.
  • Pregnant women who visited this country while pregnant, or who become pregnant within 8 weeks of leaving this country, should contact their GP, obstetrician or midwife for further advice, even if they have not been unwell.

I think we are beginning to build up a case that suggests Thailand may be no greater risk than many other countries pregnant women are visiting.

1] The reported cases in Thailand in the first 9 months of 2016 are 349 (assuming since January includes January.)

2] The Thai population is over 68M

3] The level of non-reporting is not known

4] Foetuses are more susceptible closer to conception than later (my assumption, see Figure 3). However experts don't know whether you're at higher risk if you get infected during a particular trimester.

5] A model using data from a Zika outbreak in French Polynesia estimated the risk of microcephaly in children born to mothers who acquired Zika virus in the first trimester to be 1%

6] With 4], later in pregnancy might be safer than indicated by 5]. However microcephaly is not the only birth defect to consider, though it seems the others are generally less severe (eg impairment of hearing and/or vision) though sometimes more severe (eg fatal).

7] On the other hand most babies born to pregnant women who get Zika appear to be healthy

8] The model may not be accurate or may not otherwise apply to Thailand. Experts don't know how likely your baby is to have birth defects if you get Zika during pregnancy.

9] CDC do not at present have a watch, alert or warning for Thailand

10] Travel Health Pro has:

This country is considered to have a high risk of ZIKV transmission. Increasing or widespread transmission has been reported. Pregnant women are advised to postpone non-essential travel until after pregnancy. Details of specific affected areas within this country are not available.

Judging by other usage of "non-essential travel" in health and safety warnings, coupled with no emboldening and no "very strongly" or "strongly" in front of "advised", this is barely more than a routine caution - almost obligatory from such a body and more akin to telling a child to be careful when crossing the road, rather than not to stick metal objects into power sockets.

CDC's wording is an even milder consider postponing:

women who are pregnant or planning to become pregnant should discuss their travel plans with their doctor and consider postponing nonessential travel to Thailand.

11] A combination of the above would suggest to me odds of around 1 in 100M per annum and better than that with proper precautions (DEET, no perfume, covering up at dusk and dawn avoiding areas of standing water, trying to stay indoors and high up, nets etc). Much longer than the chances of winning the lottery.

12] You will presumably be in Thailand for weeks rather than long-term, hence limit your exposure

13] If Aedes aegypti breeds like the malarial mosquito (malaria risk in Thailand estimated at 1:50,000) the rainy season is the time of highest risk, and that for Thailand usually ends in November, so you would be there after that.

HOWEVER, you must at least listen to what your doctor says as your medical history is relevant (eg will this add to a stress issue).

To take your questions in turn:

When during pregnancy will Zika cause harm to baby?

There is risk throughout pregnancy (see Comment below).

Do 100% of all bites lead to Zika?

Definitely not (eg there are other mosquitoes and insects that bite).

Is it likely we have a immunity?

My guess is no, but it does effect some people more than others. Once you've been infected with Zika, you're likely to have immunity from the virus but if so, how long for is not known.

are not all mosquitos carriers?

Not all mosquitoes are carriers. Not only does it depend on their species but also their gender.

See also: Is there a good and objective resource online about Zika virus?


How to avoid the contact with the mosquito that carries Zika Virus in Tropical countries

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    What basis do you have for your assumption that "Foetuses are more susceptible closer to conception than later"? It sounds like a wild guess, to me. Commented Oct 7, 2016 at 9:51
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    @pnuts A study published last Spring in the New England Journal of Medicine reported that the effects can occur at any stage of gestation, and beyond those of microcephaly and hydranencephaly including fetal death, placental insufficiency, fetal growth restriction and central nervous system injury.
    – Giorgio
    Commented Oct 7, 2016 at 13:58
  • @pnuts no, keep as is; the info keeps being enhanced by researchers and it's important to demonstrate that.
    – Giorgio
    Commented Oct 7, 2016 at 14:28

You have at least one full month untill December. Try to sell your trip so you don't lose (all) the money, and go on the trip when you are in better position. Ultimately it's up to you to take or not take the risk, but I hope you agree that it's better to stay on the safe side, especially when you can lose much more than you can gain.

  • @pnuts Spare me the truisms. Would you advise OP's wife to drink alcohol, because there's risk in everything we do, and if the kid gets FASDs, then well, that's life? You have to calculate the risk, and the consequences. Consequences of losing 2$ on bet aren't too bad, so you can bet 2$ even when you have 80% of losing, but when it comes to your child's whole life, I'd say that even 2% is high. I'm actually answering the question that is behind all the four questions OP's asking - "should we go to this trip because I don't want to lose the money?". Commented Oct 10, 2016 at 20:17

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