key: cord-0883336-xgpizl3l
authors: Kalafat, Erkan; Magee, Laura A; von Dadelszen, Peter; Heath, Paul; Khalil, Asma
title: COVID-19 booster doses in pregnancy and global vaccine equity
date: 2022-02-18
journal: Lancet
DOI: 10.1016/s0140-6736(22)00166-0
sha: e10bf822304f57fba83bbeeac712c9956037fc9a
doc_id: 883336
cord_uid: xgpizl3l

nan

Immunisation against SARS-CoV-2 with mRNA vaccines remains the most effective way of preventing COVID-19-related morbidity and mortality. Medium-term data show that the efficacy of mRNA vaccination (two doses) is robust for up to 5-6 months, as supported by immunogenicity studies. 1,2 Thereafter, the effectiveness of mRNA vaccines diminishes, and booster doses have been recommended for various high-risk groups. In 2021, the American College of Obstetricians and Gynecologists recommended booster doses for pregnant and postpartum women on the basis of their increased risk of COVID-19-related complications. 3 However, data on the durability of immune response in pregnant women are scarce.

Barda and colleagues reported the effectiveness of booster mRNA vaccines in a large population study from Israel. 4 A booster dose administered at least 5 months after the second dose significantly reduced the rate of new COVID-19 infections, hospital admissions, and severe infections in a cohort of 1 158 269 individuals with a median follow-up time of 2 weeks. Based on these results, the number-needed-toboost (NNB) to prevent one excess case of hospital admission was lower than the NNB to prevent severe COVID-19 (table) . However, for each of these outcomes, NNBs were about 20 times higher in those younger than 40 years, and 10-25 times higher in those without comorbidities, reflecting much lower absolute complication rates. Although these NNB estimates to prevent severe COVID-19 might be an overestimate for pregnant women, who have a two to three times increased risk of severe COVID-19 (compared with other women of reproductive age), even halving these NNBs based on age would mean that more than 10 000 booster doses would be required to prevent one case of hospitalisation or severe COVID-19 in pregnancy when administered 5 months after the second dose. The actual NNB to prevent hospitalisation or severe COVID-19 will be lower in the long term as the study had a median follow-up time of only 2 weeks. However, only in the presence of comorbidity would the NNBs be comparable to those for initial vaccination in pregnancy. 5 Given the current low vaccination coverage among pregnant women, efforts have rightly focused on increasing vaccine uptake in unvaccinated individuals. It remains to be seen whether campaigns to address vaccine hesitancy among pregnant women, or ensuring equitable access to vaccination more generally, are more important than the allocation of resources to the administration of booster doses. 6 Although any individual can decide to maximise their protection via booster doses, regardless of previous risk status, it is important to convey the magnitude of expected absolute effect for informed decision making (table). Algorithms assessing the risk of severe COVID-19 in pregnant women can be useful for triaging the need for boosters, 7 and for considering women who might be at even higher risk of COVID-19, such as those who might not have developed an adequate immune response to vaccination (eg, organ transplant recipients and those with acquired immune deficiencies), those who might be at increased risk of exposure to SARS-CoV-2 and other breakthrough infections (eg, healthcare workers), or those who might be at high baseline risk for severe COVID-19 (eg, those with severe obesity or pregestational diabetes).

The global shortage of vaccines and unequal distribution of the available stock raises an important ethical dilemma for giving booster doses to any group. Unvaccinated pregnant women in low-income and middle-income countries are at much higher risk of dying from COVID-19 but are also less hesitant to receive vaccination. 8 Furthermore, the absolute reduction in risk following a booster is likely to be small for most vaccinated pregnant women who do not have a comorbidity. Longitudinal profiling of immunogenicity induced by different types of vaccines in pregnant women is essential for informing booster timing. In the meantime, strategies for more equitable distribution of vaccines and reduction of vaccination hesitancy among the unvaccinated are likely to be more effective in reducing COVID-19 complications than offering boosters to all already-vaccinated pregnant women.

AK is a member of the COVAX working group and principal investigator of the PregCov trial and the

Severe COVID-19

Excess cases without boosters (per 100 000) 

Safety and efficacy of the BNT162b2 mRNA COVID-19 vaccine through 6 months

Waning immune humoral response to BNT162b2

Covid-19 vaccine over 6 months

COVID-19 vaccination considerations for obstetric-gynecologic care

Effectiveness of a third dose of the BNT162b2 mRNA COVID-19 vaccine for preventing severe outcomes in Israel: an observational study

COVID-19 vaccination in pregnancy-number needed to vaccinate to avoid harm

COVID-19 vaccination during pregnancy: coverage and safety

An internally validated prediction model for critical COVID-19 infection and intensive care unit admission in symptomatic pregnant women

SARS-CoV-2 vaccination in pregnancy: a unique opportunity for equity