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Hepatitis A vaccines effective in high-risk populations during outbreak

Two-dose hepatitis A vaccination was an effective preventive measure among HIV-positive individuals, including a high study population of men who have sex with men, during an ongoing outbreak of acute HCV, according to recently published data.

“We found that HAV vaccination was highly effective in preventing acute HAV infection during the outbreak, despite the delayed serologic response among HIV-positive individuals,” Kuan-Yin Lin, MD, from the National Taiwan University Hospital, and colleagues wrote. “Our results support HAV serologic screening and vaccination for those at-risk HIV-positive populations in the era of [combination antiretroviral therapy] scale-up.”

Since June 2015, Taiwan has experienced an ongoing outbreak of acute HAV with 1,440 indigenous cases reported as of Sept. 30, 2017. According to the researchers, up to 70% of the reported cases were MSM and up to 60% were HIV-positive patients.

To investigate the serologic response and efficacy of two-dose HAV vaccination among patients with HIV during a large outbreak of acute HAV, the researchers prospectively followed 1,533 adult patients who were seronegative for HAV and positive for HIV from June 1, 2015, to Sept. 30, 2016. Most patients were MSM (94.1%).

Among those enrolled, 1,001 received at least one dose of HAV vaccine and 532 did not. At the end of follow-up, 965 of the vaccinated patients received a second dose and completed 48 weeks of follow-up.

During follow-up, 60 unvaccinated patients and five vaccinated patients acquired HAV. Fifty of the unvaccinated patients had acute HAV and 10 were asymptomatic seroconversion. All patients with acute HAV were MSM and more than 50% had concurrent syphilis.

The incidence rate of acute HAV infection was 3.7 per 1,000 person-years in the vaccinated group and 99.3 per 1,000 person-years in the unvaccinated group.

After multivariate analysis, patients with HIV who received HAV vaccine had significantly reduced risk for HAV infection (HR = 0.04; 95% CI, 0.02-0.1) and acute HAV (HR = 0.05; 95% CI, 0.02-0.14). The prevention rate was 96% for HAV (95% CI, 90-98) and 95% for acute HAV (95% CI, 86-98).

In contrast, acquisition of syphilis during the follow-up correlated with occurrence of acute HAV infection (HR = 3.87; 95% CI, 2.34-6.42) and acute HAV (HR = 4.04; 95% CI, 2.33-7.02).

The seroconversion rate was 7.7% at 4 weeks after the first dose of vaccination, which increased to 21.1% at weeks 5 through 8, 54.2% at weeks 9 through 12, 58.5% at weeks 13 through 16, 64.2% at weeks 17 through 20, and 57.3% between week 21 and the administration of the second dose of HAV vaccine.

Results of an intent-to-treat analysis showed a seroconversion rate of 63.8% at weeks 28 through 36 and 55.4% at week 48, after administration of a second dose. After the researchers applied a last observation carried forward approach, the seroconversion rate was 71.6% at weeks 28 through 36 and 88.4% at week 48. Per-protocol analysis showed a seroconversion rate of 93.7% at weeks 28 through 36 and 94.5% at week 48.

Further adjusted analysis showed an association between seroconversion at weeks 28 through 36 with a younger age (per one-year decrease, OR = 1.08; 95% CI, 1.02-1.12) and undetectable plasma HIV RNA load (PVL) at vaccination (OR = 3.19; 95% CI, 1.32-7.68).

“Despite the delayed and suboptimal serologic response, HAV vaccination was still clinically effective in preventing acute HAV infections,” the researchers concluded. “Improved surrogates of immune status, such as higher CD4 counts, and suppressed PVL, enhanced the immunogenicity to the two-dose vaccine series.” – by Talitha Bennett

Disclosure: The authors report relevant financial disclosures.