News on booster doses and omicron, COVID-19 and women's health, outpatient treatments

Recipients of the Pfizer-BioNTech and Moderna COVID-19 vaccines are now eligible for booster doses at five months, government agencies recently announced.

On Jan. 3, the FDA amended the emergency use authorization (EUA) for the Pfizer-BioNTech vaccine to recommend a booster at five months rather than six, and the CDC followed suit on Jan. 4. On Jan. 7, the FDA also amended the EUA for the Moderna mRNA vaccine to recommend the same five-month interval. The director of the agency's Center for Biologics Evaluation and Research said that shortening the length of time between completion of a primary vaccine series and a booster dose may help improve immunity and may offer better protection against the highly contagious omicron variant. The CDC also updated its recommendations on Jan. 7.

Three research letters published by the New England Journal of Medicine offered evidence on the effectiveness of vaccination against omicron. One letter, published Dec. 30, found that patients who had had COVID-19 and were then vaccinated and those who had received three doses of an mRNA vaccine had substantial neutralizing titers against omicron but that those who were unvaccinated or had received two doses of an mRNA vaccine did not. A second letter from Israel, published Dec. 29, found that three doses of the Pfizer-BioNTech vaccine offered better neutralization of beta, delta, and omicron versus two doses, but neutralization against omicron was lower by a factor of four than against the delta variant. Similarly, the third letter, from South Africa, also published Dec. 29, found that two doses of the Pfizer-BioNTech vaccine appeared to offer reduced protection against hospital admission for infections presumed to be caused by the omicron variant (70% effective) versus the delta variant (93% effective).

In women's health news, the CDC published data in MMWR on Jan. 7 supporting the safety of COVID-19 vaccination in pregnancy. A retrospective cohort study of 46,079 pregnant women in the U.S. found no association between COVID-19 vaccination during pregnancy and preterm birth or small for gestational age at birth overall, stratified by trimester of vaccination, or stratified by number of vaccine doses received during pregnancy versus unvaccinated pregnant women. “CDC recommends COVID-19 vaccination for women who are pregnant, recently pregnant (including those who are lactating), who are trying to become pregnant now, or who might become pregnant in the future to reduce the risk for severe COVID-19–associated outcomes,” the authors wrote.

Also, an NIH-funded study published Jan. 5 in Obstetrics & Gynecology looked at 3,959 women, 2,403 vaccinated and 1,556 unvaccinated, to determine whether COVID-19 vaccination was associated with changes in menstrual cycles and found differences in change of cycle length (i.e., time between bleeding) of less than one day in adjusted analyses. No association was seen between vaccination and change in menses length. “Our findings are reassuring; we find no population-level clinically meaningful change in menstrual cycle length associated with COVID19 vaccination,” the authors wrote.

In treatment news, the FDA recently authorized two oral antiviral treatments for mild to moderate COVID-19. The combination of nirmatrelvir and ritonavir, manufactured by Pfizer, received an EUA on Dec. 22, and molnupiravir, manufactured by Merck, received an EUA on Dec. 23. Both drugs should be administered as soon as possible after COVID-19 is diagnosed and within five days of symptom onset, the FDA noted.

Nirmatrelvir and ritonavir (Paxlovid), copackaged for oral use, is indicated for adults and children 12 years of age and older who weigh at least 40 kg (80 lb), have a positive SARS-CoV-2 test result, and are at high risk for severe COVID-19. The treatment is not recommended in patients with severe kidney or severe liver impairment. In patients with moderate renal impairment, defined as an estimated glomerular filtration rate (eGFR) of 30 mL/min/1.73 m² or greater to less than 60 mL/min/1.73 m², a reduced dose of 150 mg nirmatrelvir and 100 mg ritonavir should be used twice daily for five days. No dosage adjustment is needed in patients with mild renal impairment (defined as an eGFR of ≥60 mL/min/1.73 m² to <90 mL/min/1.73 m²). Prescriptions should specify the numeric dose of each active ingredient, and clinicians should counsel patients about renal dosing instructions, the FDA said. In addition, nirmatrelvir and ritonavir should not be coadministered with drugs that are highly dependent on CYP3A for clearance or those that are potent CYP3A inducers. A fact sheet for clinicians with additional information is available on the agency's website.

Molnupiravir (available as Lagevrio in certain markets outside of the U.S.) is indicated for adults with a positive viral test result who are at high risk for progression to severe disease and for whom other treatment options are unavailable or clinically inappropriate. It is not to be used in patients younger than 18 years of age because it affects bone and cartilage growth and is not recommended for use in pregnancy, the FDA said. A fact sheet for clinicians with additional information is available on the agency's website. On Dec. 30, the NIH updated its outpatient treatment guidelines on therapies for high-risk patients with mild to moderate COVID-19 to include recommendations on use of these newly authorized drugs.